1. Field of the Invention
The present invention relates to a frame synchronization method, and more particularly, to a frame synchronization method which can reduce operation quantity required for frame synchronization by stopping a correlation operation, which is performed by a frame synchronizer to check for synchronization failures (out-of-sync) after the acquisition of frame synchronization, and re-starting frame synchronization upon detecting the out-of-sync state of frames using a correlation value from a despreader, and a receiver for a communication modem using the same.
2. Description of the Related Art
Transceivers for common communication modems embed data with a specific pattern and a fixed length in a packet stream as a synchronous signal and transmit it, so that receivers can recognize frame boundaries between packets.
The synchronous signal is located at the beginning of a packet in general and is thus referred to as a header. A receiver determines the start position of a packet frame by looking up a synchronous pattern corresponding to a packet header in a received bit stream. Based on the determination result, the receiver interprets the received frame to be the same as a frame structure when it was transmitted, thereby restoring original information transmitted.
FIG. 1 illustrates a transceiver for a communication modem, which receives and transmits data according to the related art spreading method.
Referring to FIG. 1, a transmitter 110 includes a serial-to-parallel converter (S/P) 112, a spreading code generator 114, and a preamble generator 116. A receiver 140 includes an analog front end (AFE) 142, a frame synchronizer 114, and a despreader 146.
The S/P 112 determines the number of bits used to select a spreading code for transmission (Tx) data Tx_data. The spreading code generator 114 selects and outputs a spreading code according to the input.
A multiplexer (MUX) 120 combines a preamble output from the preamble generator 116 and the selected spreading code into reception (Rx) data and transmits it. The reception data is distorted while passing through a communication channel 130, and is input to the receiver 140 with noise inserted therein.
The AFE 142 performs clock synchronization on the input reception data, and compensates for distortions and removes noise through filtering. The frame synchronizer 144 estimates an accurate preamble location in the input reception data stream, and the despreader 146 despreads the reception data to restore transmission data TX_data′.
However, despite the presence of the synchronous signal, the related frame synchronizer 144 performs correlation operations continuously in order to monitor the out-of-sync state of frames, thereby undesirably increasing operation quantity and system load.